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university:courses:electronics:electronics-lab-4 [07 Nov 2018 09:17]
Hannah Rosete Updated the breadboard connections as well as the Scopy plot. Changed the phase from 270 degrees to 90 to follow the set-up in Scopy as what the direction has stated. Interchanged the positions of 1+ and 1- to correctly plot the IE vs VBE Scopy plot. Chan
university:courses:electronics:electronics-lab-4 [26 Jan 2021 15:32] (current)
Doug Mercer [For further reading on the Howland current source:]
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-====== Activity ​4. A BJT Curve Tracer ======+====== ActivityA BJT Curve Tracer ======
  
 ===== Objective: ===== ===== Objective: =====
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 ===== Directions and Setup: ===== ===== Directions and Setup: =====
  
-Build the simple curve tracer circuit shown in figure ​1. The green boxes indicate where to connect the ADALM2000. Using the custom waveform editor in the Scopy AWG tool, construct a stair-step waveform with 5 levels. Be sure to reset so that you are starting with flat line at 0%. First set the type to constant. Then with start set to 0%, length set to 20% and offset set to -100% click on generate function. There should now be a line at -100% from 0 to 20%. Next change ​the start to 20% and the offset to -50% and then click on generate function again. There should now be a line at -50% from 20% to 40%. Next set the offset to +50% and the start to 60% and then click on generate function again. There should now be a line at 0% from 40% to 60% and a line at 50% from 60% to 80%. Finally set the offset to 100% and start to 80% and click on generate function one last time. There should now be a final line at 100% from 80% to 100%. Click on save and your new waveform should be in channel 2. Now at this point set the frequency to 40Hz, the amplitude to 2 V and the offset to 2.6 V. The waveform in the display should start at 0.6V and increase in 1 V increments to 4.6 V (0.6, 1.6, 2.6, 3.6, 4.6) Each step should ​be 5 mSec long for a total of 25 mSec. In AWG channel ​1 configure a triangle wave with an amplitude of 2.5 V and an offset of 2.5V (wave should swing from 0 to 5V). Set the frequency to 200 Hz ( 5 times the 40 Hz of channel 2). Comparing the waveforms in channel ​1 and channel ​2, the triangle wave in channel ​1 should go through one cycle from 0 to 5 V and back to zero during the time of one step in the waveform in channel ​2. It will probably be necessary to set the phase of channel ​1 to 90 degrees to make them line up in this way.+Build the simple curve tracer circuit shown in Figure ​1. The green boxes indicate where to connect the ADALM2000. Using the Scopy Signal Generator ​tool, in Channel 2  Buffer tab import ​the csv file for the stairstep signal needed. 
 +Now at this point set the amplitude to 2 V peak-to-peak ​and the offset to 2.6 V. The waveform in the display should start at 0.6V and increase in 1 V increments to 4.6 V (0.6, 1.6, 2.6, 3.6, 4.6). For each step to be 5 mSec long for a total of 25 mSec, set the sampling rate 200 Hz. 
 +In Signal Generator Channel ​1 configure a triangle wave with an amplitude of 5V peak-to-peak ​and an offset of 2.5V (wave should swing from 0 to 5V). Set the frequency to 200 Hz ( 5 times the 40 Hz of channel 2). Comparing the waveforms in Channel ​1 and Channel ​2, the triangle wave in Channel ​1 should go through one cycle from 0 to 5 V and back to zero during the time of one step in the waveform in Channel ​2. It will probably be necessary to set the phase of Channel ​1 to 90 degrees to make them line up in this way. 
  
-You should export your newly created stair-step waveform to a .csv file for future use. 
  
 ===== Procedure: ===== ===== Procedure: =====
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 <WRAP centeralign>​ Figure 15, Circuit to measure V<​sub>​BE</​sub>​ breadboard connection </​WRAP>​ <WRAP centeralign>​ Figure 15, Circuit to measure V<​sub>​BE</​sub>​ breadboard connection </​WRAP>​
  
-The generator output W1 should be configured for a 100 Hz triangle wave with 2 volt amplitude and -2 volt offset (for an NPN device). The single ended input of scope channel 2+ is used to measure the voltage at the base of the transistor (optionally connect 2- to the emitter to remove any input offset of the op-amp). The setup should be configured with channel 1 connected to display the output of W1 and channel 2 connected to display the base voltage. The emitter current is calculated as the voltage of W1 / 1KΩ.+The generator output W1 should be configured for a 100 Hz triangle wave with 2 volt amplitude ​peak-to-peak ​and -2 volt offset (for an NPN device). The single ended input of scope channel 2+ is used to measure the voltage at the base of the transistor (optionally connect 2- to the emitter to remove any input offset of the op-amp). The setup should be configured with channel 1 connected to display the output of W1 and channel 2 connected to display the base voltage. The emitter current is calculated as the voltage of W1 / 1KΩ.
  
 ===== Procedure: ===== ===== Procedure: =====
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 This same circuit can be used to measure PNP devices by simply configuring the ramp signal to be positive, i.e. from 0V to the maximum positive swing of the source. This same circuit can be used to measure PNP devices by simply configuring the ramp signal to be positive, i.e. from 0V to the maximum positive swing of the source.
  
 +<WRAP round download>​
 +** Lab Resources:​**
 +  * Fritzing files: [[downgit>​education_tools/​tree/​master/​m2k/​fritzing/​bjt_curve_bb | bjt_curve_bb]]
 +  * LTSpice files: [[downgit>​education_tools/​tree/​master/​m2k/​ltspice/​bjt_curve_ltspice | bjt_curve_ltspice]]
 +  * Stairstep signal: [[downgit>​education_tools/​blob/​master/​m2k/​import_waveforms/​waveforms_sg/​stairstep.csv | stairstep]]
 +</​WRAP>​
 ==== For further reading on the Howland current source: ==== ==== For further reading on the Howland current source: ====
  
-[[http://​www.cirrus.com/​en/​pubs/​whitePaper/​199210-Apex-Versatile_current_source_circuits.pdf|http://​www.cirrus.com/​en/​pubs/​whitePaper/​199210-Apex-Versatile_current_source_circuits.pdf]] +[[adi>static/​imported-files/​application_notes/​236037846AN_843.pdf|http://​www.analog.com/​static/​imported-files/​application_notes/​236037846AN_843.pdf]]
- +
-[[http://​www.analog.com/​static/​imported-files/​application_notes/​236037846AN_843.pdf|http://​www.analog.com/​static/​imported-files/​application_notes/​236037846AN_843.pdf]]+
  
 [[http://​michaelgellis.tripod.com/​howland.html|http://​michaelgellis.tripod.com/​howland.html]] [[http://​michaelgellis.tripod.com/​howland.html|http://​michaelgellis.tripod.com/​howland.html]]
university/courses/electronics/electronics-lab-4.1541578664.txt.gz · Last modified: 07 Nov 2018 09:17 by Hannah Rosete